Ignition apparatus and method of making the same



Aug. 15, 1944. T. TOGNOLA IGNITION APPARATUS AND METHOD OF MAKING THESAME Filed July 9, 1940 INVENTQFg 7 BY M ATTORNEY Patented Aug. 15, 1944IGNITION APPARATUS AND METHOD OF MAKING THE SAME Tullio Tognoia, Sidney,N. Y., assignor to Bendix Aviation Corporation, South Bend, Ind., acorporation of Delaware Application July 9, 1940, Serial No. 344,508

30 Claims.

This invention relates to ignition apparatus, and more particularly tospark plugs adapted for use in the ignition systems of internalcombustion engines and methods of making the same. I

One of the objects of the present invention is to provide a novel sparkplug adapted to withstand high operation temperatures and one whereinelectrical losses and gas leakage are substantially eliminated.

Another object of the invention is to provide a novel heavy duty sparkplug employing a unitary insulator around the center electrode made ofceramic or similar material and a novel method for fabricating the same.

Still another object is to provide a novel ceramic spark plug havingreplaceable center and ground electrodes.

A further object is to provide a novelty constructed spark plug whereinthe conduction of heat from the center electrode to the outer shell ofthe plug is facilitated.

A still further object is to provide a spark showing another form ofspark plug embodying features or the invention; and,

Fig. 4 is a sectional view similar to Fig. 1 of a portion of a modifiedform of spark plug embodying novel electrodes.

Three embodiments of the invention are illustrated in the drawing, byway of example, in the form of radio-shielded spark plugs of the generaltype now' commercially used in aircraft engines. It will be understood,however, that the invention is equally applicable to unshielded sparkplugs and other types of shielded spark plugs. To render either of theillustrated plugs unshielded, it is only necessary to remove the upperportion of the shielding barrel and the v insulating lining therefor andprovide a suitplug which is so constructed as to minimize thepossibility of undesirable flash-overs therein and gas leakagetherethrough.

Another object is to provide a novel spark plug that is, in effect, aunitary structure but which may be quite readily disassembled withsuitable equipment for overhaul and repair.

Another object is to provide a spark plug constituted by a small numberof simple and yet rugged parts and wherein novel means are employed forsecuring and supporting the center electrode assembly in the shell orbody.

The above and further objects and novel features of the invention willmore fully appear from the following detailed description when the sameis read in connection with the accompanying drawing. It is to beexpressly understood, however, that the drawing is for the purpose ofillustration only and is not intended as a definition of the limits ofthe invention, reference for this latter purpose being had primarily tothe appended claims.

In the drawing, wherein like reference characters refer to like partsthroughout the several views,

Fig. 1 is a sectional view taken on line l-l of Fig. 2 and illustratingone form of spark plug embodying the present invention;

Fig. 2 is a sectional view of said spark plug taken on line 22 of Fig.1;

Fig. 3 is a sectional view similar to Fig. 1

able terminal of any well-known type at the outer end of the centerelectrode.

In the form shown in Fig. 1, the invention comprises a tubular metallicshell 5, which is externally threaded at 6 for cooperation with athreaded opening in an engine cylinder (not shown) in the usual manner.Mounted in the lower end of shell 5 in any suitable manner known in theart is a ground electrode 1 which may be of any well-known type. Forpurposes to hereinafter appear, an intermediate portion of the borethrough shell 5 is somewhat enlarged to provide an annular internalshoulder 8 and 80 is still further enlarged at the upper end thereof toprovide an annular recess 9 in the assembled plug for silver solder orother suitable binding and sealing medium.

Mounted within shell 6 for cooperation with ground electrode 1 is acenter electrode in which is incorporated in a novel center electrodeassembly that is, in turn, supported by novel means in said shell. Asshown, center electrode I0 is cylindrical and is provided with anenlarged portion or collar ll adjacent the lower end or head Ilathereof, which head is positioned in spark gap relation to groundelectrode I. Said center electrode slidably extends through a centralbore in a solid one-piece insulator I! made of ceramic 12, while theupper portion of said sleeve projects outwardly a short distance beyondthe upper end of shell and has an annular groove it cut therein which ispartially within said shell. Sleeve may be made of any suitable metal,such as copper, the heat conductivity of which is relatively high andmay be applied to the insulating'body in any one of several ways. Theinsulator may, for example, have the surface thereof roughened bysuitable treatment, such as by sand-blasting, and the sleeve or collarl4 may be disposed thereon by a method known as the Schori process,which may be practiced with the apparatus and in the manner disclosed inFritz Schori U. S. Patents Nos. Re. 20,425 and 2,108,998. If desired,sleeve 14 may be shrink-fitted directly onto the insulator or onto athin layer of metal applied to the insulator by said Schori process orsimilar method. In one embodiment it has been found suitable to applythesleeve at a temperature of about 1,500 F. to obtain a .003" shrink fiton an insulator having an outside diameter of .375. Rapid heatconduction from the insulator to the metal sleeve or bushing I4 is thusassured and the gripping engagement of the sleeve on the insulatoraffords good support for the insulator and center electrode and preventsthe passage of gases and moisture.

For radio-shielding the input terminal of the spark plug, thereisprovided a metal barrel [1, preferably of relatively thin stainlesssteel which is in effect a part of the body of the plug. The outer end.of said barrel is lined with a tube or bushing ll of any suitableelectrical insulating material having a radial thickness comparable toor somewhat less than that of collar H. The lower or inner end of barrelIT has a close sliding fit over collar l4 and, if desired, over aportion of insulating body l2, and has a close sliding fit into theintermediate portion of the bore in shell 5 immediately above shoulder8. Said barrel is seated against shoulder 8 and has one or more holes ISin the wall thereof which register or communicate with groove 16 insleeve II when the latter is in abutting relation with liner 28.

The above-described parts are novelly held in assembled relation, asillustrated in the drawing, by filling groove l6, holes I! and annularspace 9 between the enlarged-bore of shell 5 and barrel I! with silversolder 20 or other suitable binding medium which is adapted to adhere tometal. As shown, liner l8 may be held in barrel I! by an internallyflanged cap portion 2| which is secured to the outer end of said barrelby any suitable means, such as by solder 22, and is threaded forattachment with a well-known type of radio-shielded supply cable (notshown). Any of many well-known means may be employed for this latterpurpose.

In order to insure against gas leakage from the engine cylinder alongelectrode l0 and against the entrance of moisture and the resultingpossibility of flash-overs from washer or terminal l3 to groundedmetallic parts of the spark plug, a space 23 between the upper portionof electrode l0 and insulating body l2 and the space 2| betweeninsulator l2 and liner" are filled with a suitable high heat resistant,electrical insulating material 25. Preferably, this material is put intothe plug under vacuum in liquid form and later dried or set by heatingor baking to thus avoid the trapping of air and so that all voids orspaces between the assembled parts will be filled with the same. A novelmethod of injec in the 76 insulating compound 25 into the spark plug isfully described and claimed in my U. S. Patent No. 2,348,427. Onecompound or resin which has been found suitable for use in the aboveconnection has a cashew nut shell oil base and when dried by proper heattreatment in accordance with the novel method described in theabove-mentioned copending application is converted into a high heatresistant yieldable solid which serves as excellent electricalinsulating means and means for preventing gas leakage and moistureaccumulation.

The above-described spark plug is preferably fabricated in accordancewith a novel method which comprises making the hollow insulating bodyI2, as by molding a ceramic material, such as porcelain, aluminum oxideor other suitable insulating material, into the desired shape. The outerand inner surfaces of said body may then b machined, if necessary, andthe surfaces, particularly those which are exposed in the completedstructure, may be glazed, if desired. Collar H, which has a slightlysmaller inside diameter than the outside diameter of insulator l2 atnormal temperatures is then heated to approximately 1500 F. and shrunkonto the insulator, either in direct contact with the insulator itselfor in contact with a thin metal coating applied to the insulator byspraying in the manner abovementioned. If desired, collar ll may bewholly applied by the so-called Schori process, preferably after thesurface of the insulator to be covered has been sand-blasted orroughened by other suitable means. By any of these methods an excellentbond or gripping action between the collar and insulator may beobtained.

The surface of groove IS in the assembled unit l2, II and the interiorof barrel ll in the vicinity of holes I! are coated with a suitablesoldering flux and, if desired, a ring of silver solder or the like maybe placed in said groove. The unit comprising the collar and insulatoris then placed in barrel l'l, 2| in abutting relation with insulatingliner l8 and the whole is inserted into shell or body member 5. With theparts thus assembled and supported in an upright position, additionalsilver solder and soldering flux are placed in annular space 8 andaround barrel H at the upper face of shell 5, and the whole is heated,preferably by electrical means, to approximately 1100 F. The solder isthus melted and fills groove I6 and annular space 9, thereby bindingbarrel l1 exteriorly to shell 5 and interiorly to collar I4. Solder 20thus acts as a binding medium to support the center electrode assemblywithin the spark plug body and to provide absolute assurance against gasleakage around the latter. Collar H together with solder 20 may beconsidered as means for securing and supporting insulator l2 andelectrode III in shell 5.

Center electrode l0 maybe inserted in the central bore of insulator I2either before or after the foregoing assembly process. If said electrodeis inserted after the soldering operation, as well as after groundelectrode I has been mounted in body 5, the prongs la of the groundelectrode may be temporarily bent outwardly a sumcient amount to allowfor the passage of collar 1 l or other larger portion of the centerelectrode. Said prongs may be properly adjusted after the insertion oielectrode I0. When the latter has been inserted, the plug is placed in avacuum chamber and insulating compound 25 is injected in a liquid stateafter evacuation of r the air. The plug is then taken out of the vacuumchamber, excess compound is removed, and a washer I3 is installed in asuitable press. Thereafter, the plug is placed in an oven for heattreatment of the insulating material 25 in the manner fully set out inthe above-mentioned copending application. When the particular compoundreferred to above is used, the baking temperature is preferablyincreased at intervals over a period of approximately 88 hours fromapproximately 200 F. to a. maximum of approximately 500 F., thetemperature being maintained at all times below the boiling point of thecompound, which boiling point gets higher as the compound dries.

Insulating material 25 is preferably of such a nature that it does notbecome brittle when it sets and does not shrink appreciably during thedrying process. The spaces between various parts of the plug will thusbe completely filled and, hence, obviate gas leakage as well as theentrance of moisture, both of which are conducive to the occurrence ofundesirable flashovers between the center electrode and the groundedparts of the plug. when such a compound is use'd," it is an easy matterafter solder shell 26 having an annular internal shoulder or seat 21therein and a ground electrode 20 mounted in said shell. A single,one-piece insulator 29 surrounding a center electrode 30 has a thincoating ll of metal applied to a central portion of the outer surfacethereof by the so-called Schori process or other suitable method and asleeve 32 of comparatively soft metaL-such as copper, shrunk onto saidcoating. Sleeve 32 is provided with an external flange 33 that rests onshoulder 21 and is engaged by the lower end of a nut 34 threaded intothe outer end of shell 26 and having an upwardly extending shieldingbarrel 35. Flange 53 serves as a gasket to prevent gas leakage aroundthe center electrode assembly as well as means for supporting thelatter. An insulating material, such as compound 25, may be injected inthe manner abovedescribed into the minute spaces between the upper endof electrode 20 and insulator 29 and between said insulator and aninsulating liner 36 in barrel to obviate gas leakage along saidelectrode and to avoid the possibility of undesirable flash-overs.

In order to provide further assurance against gas leakage between collar32 and insulator 29, the outer end of said collar may be provided withan enlarged bore to form an annular space 31 in which a suitable sealingmaterial 38 may be compacted. One material found suitable for thispurpose may be prepared by impregnating asbestos with liquid polymer ofcashew nut shell oil, drying the impregnated material at approximately300 F., and then grinding the same into powderform. Before the powder ispressed into recess 31, it may be heated to a gluey state.

If desired, the gluey material-may be pressed 7 into the recess beneatha rigid washer ll, and the end ll of collar 22 may be spun in to holdthe washer and material in place. It will be understood that the sealingmeans thus provided in the spark plug of Fig. 3 may also be incorporatedin the other forms of plugs illustrated.

A third embodiment of the invention which involves novel electrodestructures is illustrated. with parts broken away, in Fig. 4. As shown,a novel center electrode constituted by a ferrous alloy body portion ll,having a platinum tip 42 fused to the lower end thereof, is mounted inthe manner heretofore described in a molded ceramic insulator VM onwhich is shrunk or spray-coated a metallic collar 44. The lower end ofsaid collar engages a gasket 45 resting on an internal shoulder orflange 45 in a tubular shell or body 41. Collar N, which is preferablymade of some durable material, such as stainless steel, is provided witha flange II that fits into an enlarged portion of shell 41 and isengaged by a nut 45 threaded into shell 41 to press the collar againstgasket 45 and thus form a gas-tight seal. Nut 49 may be provided with anupwardly extending shielding barrel lined with suitable insulation thesame as is nut 34 in the embodiment of Fig. 3.

Mounted in the lower end of shell 41 for cooperation with electrode ll,42 is a novelly constructed ground electrode which, as shown, comprisesa ring or annular portion 50 having a plurality of inwardly anddownwardly projecting prongs 5|. Mounted in each of said prongs, such asby silver soldering, is a platinum pinlike member or electrode 52 whichis horizontally disposed and extends radially with respect to theplatinum tip of the center electrode and into spark gap relationtherewith.

There is thus provided a novel spark plug which is capable ofwithstanding high temperatures during long periods of use withoutappreciable deterioration of any of the parts therein, and wherein gasleakage and moisture accumulation, which initiate electrical losses, aresubstantially eliminated. Additionally, there is provided a novel methodof making spark plugs so that both the ground and center electrodesthereof may be removed with comparative ease for reconditioning orrenewal without destroying the more durable and more expensive parts ofthe structure. Novel means are also provided for preventing gas leakagebetween the parts of the center electrode assembly' of a spark plug.Furthermore, the invention comprehends novel electrode structures for aspark plug which materially increase the emciency and operating life ofthe plug.

Although only a limited number of embodiments and modifications of theinvention are illustrated and described, it is to be expresslyunderstood that the same is notlimited thereto.

For example, various features of the different embodiments illustrated,such as the electrode structure of Fig. 4, the sealing means of Fig. 3,and the coating and collar construction ii and 12 of Fig. 3 may beincorporated in other embodiments of the invention. Various otherchanges may also be made in the design and arrangement of partsillustrated, as well as in the materials suggested without departingfrom the spirit and scope of the invention as will now be apparent tothose skilled in the art. For a definition of the limits of theinvention, reference is had primarily to the appended claims.

What is claimed is:

1. In a spark plug, the combination of insulating means for a centerelectrode, a tubular metallic body member, means including a collarhaving a shrink fit on said insulating means for supporting the latterin said body member and means extending into a groove in said collar forsupporting the latter in said body member.

2. In a spark plug, the combination of a unitary insulator for a centerelectrode, an annular metallic bushing having a shrink fit on saidinsulator for supporting the latter, a tubular body member for receivingsaid bushing, and a fusible solder for securing said bushing in saidbody member.

3. In a spark plug, the combination of insulating means for a centerelectrode, an annular metallic collar gripping said insulating means andhaving an annular recess in the surface thereof, a tubular shell havinga diiferential bore. a metallic tube around said collar seated on aninternal shoulder in said shell and having one or more openings inregistry with said recess, and a fusible metal substantially fillingsaid recess, openings and a space between said shell and tube forsecuring said collar, tube and shell together.

4. In a spark plug, the combination of a tubular shell, a metallic tubeslidably fitted into said shell and secured thereto by a fusible metal,such as silver solder, and an assembly slidably fitted into said tubecomprising a tubular insulator and a metallic collar fixed on saidinsulator and secured to said tube by a fusible metal, such as silversolder.

5. In a spark plug, a tubular shell, a metallic tube slidably fittedinto said shell and soldered thereto, a center electrode assemblyslidably fitted into said tube comprising a tubular insulator for acenter electrode and a metallic collar fixed on said insulator forsupporting the same and soldered to said tube, an insulating tube liningsaid metallic tube between the outer end of the latter and said collar,and a yieldable insulating material between said insulator andinsulating tube and in said insulator around said electrode.

6. In a spark plug the combination of an assembly comprising a ceramicinsulator for a center electrode and a metallic collar surrounding saidinsulator in gripping engagement therewith, a tubular metallic bodymember, means for supporting and securing said assembly in said member,a tubular metallic barrel surrounding the upper end of said assembly, aceramic insulating lining for said barrel, and insulating materialhaving a cashew nut shell-oil base filling the space between saidceramic insulator and said lining.

'7. In a spark plug having a tubular body, the combination of aninsulator for a center electrode, a metallic coating on an annularsurface of said insulator, and a metallic collar around said insulatorin gripping engagement with said coating for supporting said insulatorand electrode in said body.

8. In a spark plug having a tubular body, the combination of aninsulator for an electrode, a metallic collar fixed on said insulator,said collar having an enlarged bore at one end thereof forming anannular space with said insulator, and a compactable material pressedinto said space.

9. In a spark plug, the combination of an electrical insulator for anelectrode, a metallic coating on an annular surface of said insulator,

and a metallic collar having a shrink fit on said coating.

10. In a spark plug, the combination of an insulator for an electrode, acylindrical metallic collar fitted on said insulator, said collar havingan enlarged bore at one end thereof forming an annular space with saidinsulator, and a heatresistant material packed in said space to form agas seal.

11. In a spark plug, a tubular shell, 9. ground electrode mounted insaid shell and comprising an annular member having an inwardly anddownwardly projecting prong and a horizontally extending pin-like membermounted on said prong, a center electrode comprising a ferrous alloybody portion and a platinum tip fused to said body portion, and meansfor supporting said center electrode in said shell with said tip inspark gap relation with said pin.

12. In a spark plug, a tubular shell, a ground electrode mounted in saidshell comprising an annular ferrous alloy member having a plurality ofcircularly arranged prongs and a radially extending pin-like platinummember mounted on each of said prongs, a center electrode comprising aferrous alloy body portion and a platinum tip, and means for supportingsaid center electrode in said shell with said tip extending between theinner ends of said pin-like members.

13. In a spark plug, the combination of insulating means for anelectrode, a tubular metallic body member, and means including a sprayedmetallic collar on said insulating means for supporting the latter insaid body member.

14. In a spark plug having a tubular shell, the combination ofinsulating means for insulating an electrode from said shell, and meansfor supporting said insulating means in said shell comprising a sprayedmetallic coating on the outer surface of said insulating means.

15. The method of making a spark plug which includes the steps of makinga tubular insulator having an annular portion of the outer. surfacethereof roughened, applying an annular metallic coating on saidroughened surface, and shrinkfitting a tubular metallic collar on saidcoating.

16. The method of making a spark plug which includes the steps of makinga tubular insulator, inserting a center electrode in the bore of saidinsulator, and filling an annular space between said electrode andinsulator with a pliable material having a cashew-nut-shell oil base.

17. The method of making a spark plug which comprises the steps ofmaking a tubular insulator, fixing a tubular metallic collar on saidinsulator, inserting a center electrode in the bore of said insulator,filling an annular space between said electrode and insulator with achemically setting liquid, securing said electrode and insulatortogether, and baking the assembled parts until said liquid sets as asolid.

18. In a spark plug having a tubular body member, the combination ofinsulating means for a center electrode. a metallic cylindershrinksulator for an electrode, a metallic cylinder hav-,.

ing a shrink-fit on said insulator, a tubular metallic body forreceiving said cylinder, and means engaging a groove in said cylinderintermediate the ends thereof for securing said body and cylindertogether for positioning said insulator in said body.

20'. In a spark plug, the combination of a unitary ceramic insulator foran electrode having an external wall portion of substantially uniformdiameter, an annular metallic collar fixed on said wall portion forsupporting said insulator, a tubular shell, and means for securing saidcollar in said shell, said 1astnamed means including means having afused bond with said shell.

21. In a spark plug, the combination of a univ tary insulator for anelectrode, an annular metallic bushing fixed on said insulator forsupporting the same, a tubular body member for receiving said bushing,and fusible means engaging said bushing and member for securing saidbushing in said member.

22. A spark plug comprising insulating means fior a center electrode, ametallic cylinder having a shrink-fit on a portion of said insulatingmeans having a uniform outside diameter whereby said insulating means issupported, a tubular shell, and means including means having a fusedbond with said shell for supporting said cylinder in said shell. I

23. A spark plug comprising a tubular shell, insulating means for acenter electrode, a metallic cylinder having a shrink-fit on saidinsulating means for supporting the latter, and fusible means havinginterlocking engagement with said cylinder for supporting the latter insaid shell.

24. A spark plug comprising a tubular shell, a metallic tube extendinginto said shell, a metallic sleeve in said shell and tube for supportinginsulating means for a center electrode, and fusible meansfor securingsaid shell, tube and sleeve in fixed relation to one another.

25. In apparatus of the class described, a tubular metallic shieldingbarrel, an insulating liner in said barrel, and means secured to the endof said barrel including a cylindrical portion engaging the externalsurface of the barrel and an internal flange having an internal diameterapproximately the same or less than the internal diameter of saidinsulating lining.

26. A spark plug comprising insulating means for a center electrode, ametallic sleeve surrounding said insulating means, and a substancecomprising asbestos filling an annular space between said sleeve andinsulating means.

27. A spark .plug comprising insulating means for a center electrode, ametallic sleeve surrounding said insulating means, and a substancecomprising asbestos and a cashew-nut-shell oil product filling anannular space between said sleeve and insulating means.

28. In a spark plug having a center electrode, the combination of atubular shell, an annular member mounted in said shell and having abendable prong thereon, and a pin-like member mounted on said prong andextending into spark gap relation with said center electrode.

29. A spark plug comprising a tubular shell,

insulating means for an electrode, a metallic sleeve around saidinsulating means for supporting the same, and means for securing saidsleeve in said shell including a tubuiar element extending into saidshell and joined thereto by fusible means.

30. In a spark plug, a tubular metallic shell, .tubular insulating meansfor an electrode, an

and tube.

TULLIO TOGNOLA.

